Process of producing a planographic printing plate and resultant article

ABSTRACT

Planographic printing plates and continuous planographic printing forms having a flexible foundation supporting a planographic printing layer and process of making are disclosed. The flexible foundation is an opaque, thin sheet or continuous web or strip of synthetic thermoplastic polymer having uniformly rough, receptive surfaces, the foundation being selected from unicellular foamed film or normally-clear, normally-smooth film treated on both surfaces with volatile organic solvent having a dissolving power therefor. One surface of the film foundation is coated with a thin planographic layer.

United States Patent Newman [451 May 16, 1972 [54] PROCESS OF PRODUCINGA PLANOGRAPHIC PRINTING PLATE AND RESULTAN T ARTICLE [72] Inventor:Douglas A. Newman, Glen Cove, NY.

[73] Assignee: Columbia Ribbon and Carbon Manufacturing Co., Inc., GlenCove, NY.

[22] Filed: Apr. 6, 1970 [21] App1.N0.: 26,091

Related US. Application Data [63] Continuation-impart of Ser. No.800,414, Feb. 19,

1969, abandoned.

[52] U.S.Cl ..117/4,96/33,10l/401.1, 101/453, 101/460, 117/47 A, 117/68,117/76 F,

117/138.8 R, l17/l38.8 UA,117/138.8 E

[51] 1nt.Cl. ..B44d 1/14,B4ln H12 [58] FieldofSearch..117/76F,70R,l38.8UA,138.8R, 117/98 F, 47 A, 4; 101/453, 401.1, 460,461, 462;

[56] References Cited UNITED STATES PATENTS 2,139,214 12/1938 Wahl..l17/4X 2,384,657 9/1945 Tyler ..1 17/4 2,941,466 6/1960 Newman et al....l0l/46O 3,055,295 9/1962 Perkins 10 l /462 3,250,731 5/1966 Buhl eta1 ..264/53 3,256,810 6/1966 Ensink [01/461 3,311,497 3/1967 Park..117/47 X 3,470,013 9/1969 Wagner 101/453 X Primary Examiner-William D.Martin Assistant ExaminerRalph l-lusack Attorney-lohnson & Kline [5 7]ABSTRACT 7 Claims, 3 Drawing Figures PATENTEDMAY 16 m2 ooonooe ooooloooooooooo ooo oooooooecoooooooo VOOOOOOO INVENTOR. flmgylas A.Mew/27am fi 7' '04QA/EY$ PROCESS OF PRODUCING A PLANOGRAPHIC PRINTINGPLATE AND RESULTANT ARTICLE This application is a continuation-in-partof parent application Ser. No. 800,414, filed Feb. 19, 1969, nowabandoned.

Planographic printing plates conventionally have a paper foundationsupporting the planographic printing layer and are frequently used inmulti-sheet continuous forms as one of the copy sheets imaged by meansof a chain printer machine or other type printer. Images are printed onthe copy sheets by means of a ribbon and/or interposed transfer sheetsand the imaged copy sheets are then torn from the continuous strip andused for their intended purposes. The copy sheet which is a planographicprinting plate is wetted with etching fluid, mounted on a planographicprinting machine and duplicate copies are made therefrom.

In order to be useful for continuous forms use, the planographic webmust be capable of being perforated to form pinengaging holes along bothedges of the web for transport of the web through the printing machineand/or capable of being perforated with weakened tear lines separatingsuccessive plate lengths whereby each imaged plate can be torn from theweb for use in the planographic printing machine. Even for conventionaluse, many planographic printing machines require that the plate haveclamping holes or scalloped edges for clamping the plate on the printingcylinder.

Planographic printing plates, regardless of type, must have certainproperties in order to function properly in the planographic printingprocess. They must be capable of accepting and retaining water on theunimaged areas of the planographic surface. lt is the function of theplanographic layer to accept moisture but, since such layer must beporous in order to retain the oleophilic images applied thereto, theplate foundation must not absorb the water to any great extent.

Nearly all planographic printing plates have a paper foundation exceptin specialized fields such as photosensitive plates and thermographicplates. Paper is capable of being perforated and thus is the onlymaterial used for plates in the continuous forms field discussed supra.Paper, however, is normally highly absorbent of water and thus requireswet strength treatment and treatment of one or more interposed waterbarrier layers beneath the planographic printing layer to reduce thetendency of the paper foundation to absorb the water from the printinglayer. Paper plates having such treatment still absorb water to a highdegree and require continuous moistening during duplication.

Moreover such paper plates often have a tendency to curl rather thanstaying flat when the ambient conditions change and particularly whenthe ambient moisture or humidity level changes. They also have atendency to change dimensions to a small but important degree withchanges in the ambient conditions, particularly humidity. Such changesin flatness and dimensions are particularly important in certainapplications such as when the plates are used in continuous forms withmarginal perforations which must align with the web-transporting pins onthe printing machine, and when the weakened tear line perforations whichseparate plate lengths must be in registration with similar perforationson the other sheets of the form such as the transfer sheet.

It is known to use waterresistant plastic film foundations in place ofpaper foundations to produce specialized plates which are photosensitiveor transmissive of light or infrared radiation to a high degree. Suchfilms are limited to these areas because of the difficulty ofprocessing, coating, cutting, and handling plastic film and the poorreceptivity and retentivity of plastic film for planographic printinglayers. Also filmbase plates are not used in many applications includingcontinuous forms because of the difficulty of cutting and perforatingthin films or forming weakened severing lines thereon.

The present invention is concerned with providing planographic printingplates having foundations which comprise the advantageous properties ofpaper and plastic film foundations but which do not have thedisadvantageous properties of either of these materials.

This and other objects and advantages of the present invention will beapparent to those skilled in the art in the light of the presentdescription including the drawing in which:

FIGS. 1 and 2 are diagrammatic cross-sections, to an enlarged scale, ofplanographic printing plates according to different embodiments ofthepresent invention, and

FIG. 3 is a plan view of a section of a perforated continuous formplanographic printing plate according to another embodiment of theinvention.

The novel planographic printing plates of the present invention comprisean opaque, thin, water-impervious foundation 1 of syntheticthermoplastic polymer having uniformly rough, receptive surfacessupporting directly or indirectly on one of said surfaces a planographicprinting layer 3, as shown by P16. 1 of the drawing. The foundationaccording to the embodiment of the drawing comprises a foamed film whichis extruded as such and is of the closed cell or unicellular type asopposed to the open cell or sponge type. Unicellular foam films aredefined as those films having at least 50 percent of the cell content inthe form of closed cells 4. Such films are opaque in appearance and haveuniformly rough surfaces 5 which are porous and exceptionally receptiveto and retentive of planographic coatings and imaging materials. Thesurfaces 5 of such films appear relatively smooth and continuous to theeye and are substantially impervious to water.

According to another important embodiment, the foundation comprises athin, normally smooth, clear film of synthetic thermoplastic polymerwhich has been treated on both surfaces with a volatile organic solventwhich softens or dissolves the polymer at the film surfaces to renderthe surfaces frosted and opaque in appearance. The treated surfaces arerendered uniformly rough and given a surface porosity whereby they areexceptionally receptive to and retentive of planographic coatings andimaging materials.

The specific composition of the planographic layer 3 of the presentplates is not critical to the invention since the receptive film supportprovides advantages over the use of paper and conventional plastic filmsupports regardless of the nature of the planographic layer and whetherit is electrostatic or sensitive to light of heat. Planographic layershaving a hydrophilic-oleophilic balance are generally applied as aqueousdispersions containing a hydrophilic film-forming binder material,cross-linking agent to insolubilize the binder, filler, wetting agents,pH modifiers and other ingredients such as zinc oxide in electrostaticplates and photosensitive materials in photosensitive plates. Thefollowing US. patents are incorporated by reference insofar as theplanographic compositions and coating procedures thereof are suitablefor preparing plates according to the present invention in which theopaque, porous-surface-film support is used in place of prior-knownsupports: US. Pat. Nos. 2,534,650; 2,941,466; 3,055,295; 3,256,810; and3,323,451.

The foamed-film foundations suitable for use according to one embodimentof this invention are extruded under pressure in conventional mannerfrom foam-forming compositions comprising a synthetic thermoplasticresin, a blowing agent and, preferably, a nucleating agent. Fillers andcolorants may be included as desired. The composition is generallyextruded in the form of an expanded tube which is then flattened,trimmed, cut into sheet or web dimensions and separated.

The preferred resin is polystyrene which is commercially available inthe form of expandable polystrene pellets which contain the blowingagent and other ingredients which assist to expand the melted polymerinternally. However a variety of other resins may be used includingacrylic polymers and copolymers, butadiene copolymers, hydrocarbonpolymers such as polyethylene and polypropylene, polymers and copolymersof styrene derivatives, and the like. The following United Statespatents are incorporated by reference insofar as they relate toexpandable resin compositions and the production of foamed filmssuitable for use according to the present invention: US. Pat Nos.3,121,760; 3,248,462; 3,250,731; and 3,287,477.

The foamed films suitable for use herein are unicellular, i.e., have atleast 50 percent of their cell content closed, are light in weight inthat they contain at least about 10 percent of their volume in the formof gas within the cells and have a thickness of from about 1 mil up to10 mils and preferably from about 3 to 6 mils.

The following examples are given by way of illustration and should notbe considered limitative.

A web of expanded polystyrene is produced according to Example 1 of US.Pat. No. 3,248,462 and has a thickness of about 4 mils (0.004 inch). Theweb is light in weight in that over half of its thickness comprises gastrapped within the cell structure. The web is also opaque white inappearance due to the cell structure. Referring to the present drawing,the foamed film 1 comprises an expanded matrix 2 of the polystyrenebinder containing a multiplicity of closed cells 4. The surfaces 5 ofthe film are rougher and substantially less smooth than a cast,homogeneous film although the surfaces appear relatively smooth to thenaked eye.

The web is converted into a planographic printing plate by applying theplanographic layer directly thereto or by first applying a hydrophilicunderlayer. The underlayer is most important in cases where the platemust be correctable. If erasures are made on the planographic layer, aportion of the layer may be eroded and therefore it is important to havea hydrophilic layer beneath. Such layers are well known in theplanographic plate art.

According to the embodiment of FIG. 1 of the drawing, the followingplanographic composition is applied directly to the surface of thefoamed film in a weight of 8 pounds per ream (3,300 sq. ft.) and driedin conventional manner.

lngredients Parts by Weight Polyvinyl alcohol 2.0

Syton (40% aqueous colloidal silica) 12.0 Glyoxal (40% aqueous solution)0.5 Clay 16,0 Alum aqueous solution) 10.0 Zinc acetate 4.0 Acetic acid(25% aqueous solution) 0.2 Water 55.3

The dried planographic layer 3 firmly anchors to the relatively roughsurface 5 of the foundation and resists picking or peeling therefromduring flexing and use.

According to the embodiment of FIG. 2, the foamed-film foundation isfirst coated with the following hydrophilic composition in a weight ofabout 4 pounds per ream and dried in conventional manner.

The dried undercoating 6 is hydrophilic and the planographic layer 7 isapplied thereover in the manner discussed supra in connection with theplate of FIG. 1.

The coated webs having the structure shown by either FIG. I or H0. 2 canthen be cut into sheet lengths for use in conventional manner or may beperforated in conventional manner for use as a continuous strip or forcollation into a multi-sheet continuous form. FIG. 3 of the drawingillustrates a continuous strip 8 of plate according to this inventionand shows the planographic surface 9, marginal feed perforations l0 andweakened tear perforations 11 for separating sheet lengths.

Solvent-treated film foundations may be employed in place of the foamedfoundation of the examples recited hereinbefore. Such films are producedby providing conventional thin,

clear films of synthetic thermoplastic polymer, treating the surfaceswith volatile solvent to cause surface dissolution of the films, andthen evaporating the solvent to provide films which are opaque inappearance and having uniformly rough surfaces which are porous andreceptive. The film and solvent should be selected so that the solventis not such an active solvent for the film that the internal strength ofthe film is destroyed. Solvent action must be limited to the filmsurface so that only surface porosity is produced and rupture of thefilm is prevented. Dilute solvent solutions may be used and/or theduration of exposure of the film to the solvent may be restricted toproduce the desired results. This latter result may be accomplished byimmersing the solvent-treated film into a non-solvent at the desiredtime to instantaneously stop the solvent action. For instance a smooth,thin, clear film of polystyrene film, such as Dow Trycite, may beimmersed into a solvent bath comprising a 5 percent solution of acetonein water for a period of 1 second and then immediately immersing thetreated film in Water to stop the solvent action and produce an opaquepolystyrene film having the desired surface porosity.

Such solvent-treated films are found to have the appearance, feel, andcutting properties of paper while retaining the flexibility, strength,and impervious nature of plastic film. They can be marked, coated, cut,perforated, and punched as easily as paper and thus function perfectlyaccording to the present invention.

Because of the receptivity of the present film supports for coatings,the present plates are particularly well adapted for the application ofa pressure-sensitive transfer layer to the surface thereof opposite theplanographic surface. Reference is made to my US. Pat. No. 3,274,928relating to such bifunctional plates. The application of a conventionalcopying layer is particularly useful when the present plates are used inmultisheet forms whereby a carbon copy or duplicate planographicprinting plate is produced simultaneously with the imaging of theinstant plate. The presence of the carbon transfer layer on the back ofthe plate avoids the necessity of interposing a separate carbon paper inthe form. The reduced thickness and also the pressure-deformability ofthe present plate foundations makes it possible to produce sharper andclearer images on the plate surface and on the underlying copy sheet orsheets.

Plates in sheet or continuous strip form produced according to thepresent invention have excellent dimensional stability. They are flatand resist curling under the effects of changes in the ambientconditions such as increases or decreases in humidity. They do notabsorb moisture and therefore the plates neither shrink nor expand toany important extent under the effects of changes in humidity and/ortemperature. Therefore any perforations made in such plates such as forpurposes of transporting continuous strips thereof or for tearing suchstrips into sheet lengths or for mounting such plates on a planographicprinting drum remain accurate in position under varying atmosphericconditions.

Variations and modifications may be made within the scope of the claimsand portions of the improvements may be used without others.

I claim:

1. The process of producing a planographic printing plate whichcomprises the steps of:

a. treating both surfaces of a normally clear, normally smooth syntheticthermoplastic film foundation with a volatile organic solvent having adissolving power for said film to render said surfaces opaque anduniformly rough,

b. treating both surfaces of said solvent-treated film with a liquidwhich does not have dissolving power for said film to stop the solventaction of said organic solvent,

c. applying to one of the rough surfaces of said film a thin layer of anaqueous planographic composition comprising a hydrophilic bindermaterial, and

d. drying said layer to form a thin planographic layer having ahydrophilic-oleophilic balance.

2. A planographic priming plate produced according to the process ofclaim 1.

3. The process of claim 1 in which an aqueous composition comprising ahydrophilic binder material is applied directly to the rough surface ofthe film and dried to form a thin hydrophilic undercoating, and theaqueous planographic composition is applied over said undercoating.

4. A planographic printing plate produced according to the processofclaim 3.

5. The process of claim 1 in which the foundation is a continuous weband the coated web is cut into strip lengths and perforated to form acontinuous planographic printing strip 6. A planographic printing platewhich is dimensionally stable and moisture-impervious comprising a thin,flexible synthetic thermoplastic film foundation having uniformly roughopaque surfaces, said film being a unicellular foamed film having atleast 50 percent of the cell content in the form of closed cells, onesurface of said film foundation supporting a thin planographic layerhaving a hydrophilic-oleophilic balance.

7. A planographic printing plate according to claim 6 in which thefoundation comprises expanded polystyrene.

2. A planographic printing plate produced according to the process ofclaim
 1. 3. The process of claim 1 in which an aqueous compositioncomprising a hydrophilic binder material is applied directly to therough surface of the film and dried to form a thin hydrophilicundercoating, and the aqueous planographic composition is applied oversaid undercoating.
 4. A planographic printing plate produced accordingto the process of claim
 3. 5. The process of claim 1 in which thefoundation is a continuous web and the coated web is cut into striplengths and perforated to form a continuous planographic printing strip6. A planographic printing plate which is dimensionally stable andmoisture-impervious comprising a thin, flexible synthetic thermoplasticfilm foundation having uniformly rough opaque surfaces, said film beinga unicellular foamed film having at least 50 percent of the cell contentin the form of closed cells, one surface of said film foundationsupporting a thin planographic layer having a hydrophilic-oleophilicbalance.
 7. A planographic printing plate according to claim 6 in whichthe foundation comprises expanded polystyrene.